Since prehistoric times, when body paint was first being applied, separation of pigments and other components in paints and dyes has led to inconsistent colors and non-uniform applications of make-up. Separation and settling is a well-known phenomenon in liquid, or fluid-phase systems, that results in diminished shelf-life, non-uniform colors and ineffectual application of make-up. Separation can also take place in powder mixtures with the less dense material tending to concentrate in the upper volume of the mixture.
Advances in the cosmetic arts, and the choice of possible cosmetic formulants, are constrained and delimited by, among others, the following requirements:
compatibility, both physical and chemical, with customary cosmetic formulants and pre-cursor materials which can include both hydrophilic and lipophilic materials; PA1 stability, again both physical and chemical and also biological, in end-product formulations for extended distribution and shelf-life, especially against settling, loss of volume and spoilage; PA1 end-product stability for the consumer after opening; PA1 end-use functionality which, in addition to the more or less subtle ornamental functions required of, for example, lipstick, mascara, face powder and nail polish, includes the more elusive qualities of feel, ease of application as well as an appropriate range of adhesion; and, most importantly, PA1 non-toxicity, non-comedogenicity, hypoallergenicity and the like, in other words, dermatological innocuity. PA1 a) microsphere-material particles having a particle size less than 1000 microns; PA1 b) a plurality of pigment-material particles covalently bonded to said polymeric particles; and PA1 c) a coupling agent residue extending between said pigment materials and said microsphere particles whereby they are covalently bonded;
Many, but not all, of these properties can be related to dispersibility of the pigment materials and the art is replete with proposals for improving pigment dispersibility. Noting that a pigment can be considered as a concentrated particle of colorant or other material providing a useful visual effect, including pigment extending, techniques to improve dispersibility usually comprise grinding or milling pigment materials to a fine particle size and coating the particles.
Milling of course increases the available surface area and visual effect of the pigment, and thus its effectiveness. There are many prior art teachings relating to the coating of pigment materials to improve their dispersibility. Most pigment materials tend to have a hydrophilic surface character making them hard to disperse in organic media, and it is accordingly well-known to treat pigment materials to give them a hydrophobic character and to use surfactants, anti-flocculants and the like to improve the dispersibility of the pigment materials.
The present invention takes a new approach to the improvement of dispersibility, providing striking results of great value to the cosmetics industry. Indeed the invention Succeeds in providing some control over the spatial distribution of particulate pigment materials in subsequent cosmetic formulations.
In U.S. Pat. No. 4,877,604 to M. Schlossman there are described a number of methods to coat pigments and pigment materials with titanate coupling agents including isopropyl triisostearoyl titanate. M. Schlossman provides valuable improvements in the art of pigment material dispersibility.
In a different industry, with different constraints, the plastics industry, materials known as spherical polymeric particulates in powder form and hollow spheres in powder form, either of which materials may be called microspheres, are known as valuable fillers and are prized for their sphericity, controlled particle size and low density, see for example, Ruhno "Handbook of fillers for plastics", edited by H. S. Katz et al , pp. 437-438 Van Nostrand Reinhold (1978).
According to Ruhno, there are major advantages to the plastics industry in the ability of microspheres to act as fillers in composite materials, displacing high-priced polymers with lower density, and better density control than solid mineral fillers. Some end product advantages are uniform shrinkage, improved sandability and increased impact resistance.
A brief review of the history and development of spherical polymeric powders or microspheres, including hollow spheres, sized under 1000 micron, can be found in the Ruhno reference. Inorganic and organic hollow spheres are described and referred to as "microspheres" the term being used for materials which are spherical, small and light, and in the context of this reference, hollow and polymeric. Obviously, the above-described end-product advantages are not of general use in cosmetics.
Native organic polymeric microspheres have been incorporated in cosmetic compositions to impart desirable texture characteristics of smoothness and feel, as well as pourability to powder cosmetics, notably makeup, see for example UK Patent Application GB 2 191 945. An important drawback is high oil absorption causing excessive drying and caking. Another problem is that small round microspheres do not adhere well to the skin.
Inert microspherical materials, especially organic polymeric materials, for example spherical nylon or polyethylene powder, have been employed as a cosmetic raw material, see for example, the Journal of The Society of Cosmetic Chemists, 41, 197-207, May/June 1990 ("Cosm. Chem." hereinafter). Here, hybridized powders are disclosed in which fine-chemical deodorant powders, specifically zinc oxide and aluminum chlorhydrate are mechanically layered on such microspheres by mixing and percussion in a centrifugal ball mill. The active, chemical quenching power of the deodorants is retained and improved physical properties of the deodorant powders result, including better texture and lower coefficients of kinetic friction, the latter correlating with smoothness.
Mechanofusion processes are expensive and difficult to use on a commercial scale for bulk raw materials. A drawback of such cosmetics-containing microspherical particles produced by mechanofusion processes, especially organic polymeric particles, is that they can have too high an oil absorption capacity, giving an unacceptable drying effect to the skin. Furthermore, the mechanical layering technique results in the outer powders being partially buried, reducing their exposed surface area, a drawback for pigment materials. Another difficulty may arise during pulverization when too much heat can cause polymeric microspheres to melt.
Also, while deodorants may be embraced by some interpretations of the term "cosmetic" their properties are obviously not those required for decorative cosmetics as a material used to adorn embellish or beautify the wearer, to enhance the visible appearance of exposed surfaces of the wearer, and they are not usually applied to normally exposed skin surfaces.
The Cosm. Chem. disclosure is silent as to the suitability of small inert spherical powders for inclusion in appearance-enhancing cosmetics, especially for topical application where the oil absorption and light-reflective properties of cosmetics are paramount. Nor is the Cosm. Chem. disclosure relevant to liquid phase dispersions for manual application by spreading. Certain additional properties are vital for appearance-enhancing cosmetics. These properties include not only their appearance and their ability to sustain and develop pigments, but also end-product characteristics such as spreadability.
Additionally, while the physical properties of feel and smoothness that can be contributed by microspheres in some formulations may be desirable out of the container, these are of no value if the product lacks adequate adhesion to remain on the skin. This is a further drawback of microspheres.
Broad usage of microspheres is contraindicated by high cost in addition to technical factors. Formulators may encounter difficulties during processing, for example, blending inconsistencies arising from bulk density differences; pressing problems in which oil can come out, and stability problems because prolonged oil absorption can cause dried cake, cracking, and impair the texture of the product. In addition, smooth, round particles do not adhere well to the skin.